Chemistry – Unit 5 Review
1. Definitions
a. mole
b. molar mass
c. Avogadro’s number
d. empirical formula
e. molecular formula
2. Find the molar mass of the following:
a. KNO3
d. oxygen gas
b. (NH4)2CO3
e. Ca(NO3)2
c. Ag2CrO4
f. PbSO4
3. Consider the masses of various hardware below.
Type
Mass (g)
Relative mass
Washer
1.74
Hex nut
3.16
Anchor
3.00
Bolt
7.64
a. Do the calculations necessary to complete the table.
b. Explain the connection between these calculations and the atomic masses in the
Periodic Table.
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U5 review v3.0
4. Convert from g  moles or from moles  g. Show units.
a. 12.0 g Fe x
=
moles
b. 25.0 g of Cl2 gas x
=
moles
c. 0.476 g of (NH4)2SO4 x
=
moles
d. 0.15 moles NaNO3 x
=
g
e. 0.0280 moles NO2 x
=
g
f. 0.64 moles AlCl3 x
=
g
5. Use Avogadro’s number to do the following. Show work, use labels.
a. How many atoms are there in 0.00150 moles Zn?
b. If you had 2.50 moles of oxygen gas, what mass of the gas would be in the
sample?
c. A 4.07 g sample of NaI contains how many atoms of Na?
d. How many atoms of chlorine are there in 16.5 g of iron (III) chloride, FeCl3?
*e. What is the mass of 100 million atoms of gold? Could you mass this on a
balance?
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U5 review v3.0
6. Calculate the empirical formula of a compound that contains 4.20 g of nitrogen and
12.0 g of oxygen.
7. When 20.16 g of magnesium oxide reacts with carbon, carbon monoxide forms and
12.16 g of Mg metal remains. What is the empirical formula of magnesium oxide?
8. What is the molecular formula of each compound?
Empirical Formula
Actual Molar Mass of
Compound
CH
78 g/mole
NO2
92 g/mole
Molecular Formula
9. A compound is composed of 7.20 g of carbon, 1.20 g of hydrogen and 9.60 g of
oxygen. The molar mass of the compound is 180 g/mole. Determine the empirical
and molecular formulas of this compound.
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U5 review v3.0
10. What is the % by mass of oxygen in water?
11. A compound of iron and oxygen is found to contain 28 g of Fe and 8.0 g of O. What
is the % by mass of each element in the compound?
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U5 review v3.0